U.S. Pat. No. 5,471,515, to Fossum, et. al., entitled "Active Pixel Sensor with Intra-Pixel Charge Transfer." This invention converts the photogenerated charge stored under the photogate into a voltage by transferring the charge to a sense node (typically a capacitor) located within the active pixel unit cell. Fossum then utilizes dual sample correlated double sampling of the voltage based signal to reduce signal noise and eliminate the effect of dark current from the photosensor. The voltage associated with the image exposure is then subtracted from the voltage associated with a read during a dark sample by a voltage differencing amplifier located at the end of the row or column of the photosensors. By using appropriate row and column selection transistors a subsection of the array can be read out without the need to read out the entire image array. The Fossum invention does not however allow for an increase in the overall sensitivity of the CCD detector elements, nor does it envision the utilization of an array optic type structure to form an image of different segments of the field of view, although the patent does disclose the use of a lens array for concentrating light on the active pixel. Fossum does not include means for adjusting the overall exposure level of the pixel internal to the unit cell of the detector array. Fossum is also performing most of the signal processing in a voltage amplification mode, whereas the present invention utilizes the advantages of the current mode of signal processing.
In U.S. Pat. No. 5,004,901, entitled "Current Mirror Amplifier for use in an Optical Data Medium Driving Apparatus and Servo Circuit" to Yoshimoto, et. al., photogenerated current from an optical disk tracking and read sensor is amplified in fixed steps by a switchable series of current mirrors, where the current mirrors achieve current multiplication through the use of output stages that incorporate either multiple output transistors with the bases of the output transistors connected in parallel or by the use of output transistors with emitter areas that are integral multiples of the emitter areas of the input side transistor. The purpose of Yoshimoto's invention is to allow the utilization of received photocurrents with a large dynamic range by multiplying the input current by an adjustable ratio, where the multiple current ratios are selected through a switchable network of differential amplifiers. Yoshimoto's invention is not related to the field of array image sensors and requires the use of a switchable array of differencing amplifiers. Yoshimoto's invention does not integrate the current from the photosensor and the current is continuously generated by received light from the laser light emitted by the optical disk head. Therefore, the sensor is not exposed to an image with its sensed signals being integrated by signal processing electronics, as in the current invention, but is rather used in a continuous optical disk position monitoring mode. Yoshimoto does not utilize dual slope correlated double sampling for noise reduction as disclosed in the present invention. Yoshimoto does not make any mention of the use of array optics with a field of view which varies as a function of radial position in the sensor array.